The present invention relates to a method and apparatus for making drip irrigation lines, and also to a preformed member useful in such method.
Drip irrigation lines generally include a continuous tube having a plurality of openings therethrough along spaced intervals of the tube, and a plurality of flow-reducer elements bonded to one face of the tube in communication with the openings so as to reduce the flow of the outletted irrigation water to drops or trickles. Such drip irrigation lines are gaining widespread use because of their many advantages, including efficiency in the delivery of the irrigating water directly to the plant roots, and substantial savings in the required irrigation water and/or additives thereto.
Such drip irrigation lines are generally produced at the present time by extruding the plastic tube, bonding the flow-reducer elements to the extruded tube at longitudinally-spaced intervals, and then forming the outlet openings through the tube at longitudinally-spaced intervals aligned with the outlet ends of the flow-reducer elements. U.S. Pat. Nos. 3,981,452, 5,022,940, 5,271,786 and 5,282,916 illustrate examples of such-known extrusion processes. Extrusion apparatus, however, is very expensive, and the initial cost of such apparatus therefore constitutes a substantial item of cost in manufacturing such drip irrigation lines. This is particularly true in the production of inexpensive thin-wall lines since both the initial cost, and the maximum rate of extrusion, of such apparatus are substantially the same whether thick-wall or thin-wall tubes are being extruded. In addition, high precision is required in forming the outlet openings in the tube, since any misalignment of the outlet opening with respect to the outlet end of the flow-reducer elements incorporated in the tube, will deleteriously affect the operation of the drip irrigation line.